Selective solvent extraction process in the gas-oil range



United States Patent Charles J.

There are many selective solvents for the extraction of specific hydrocarbon components from various hydro carbon systems, especially in the petroleum industry, and it is obvious that there is no one selective solvent which is adequate for all purposes. In using a selective solvent for the extraction of certain hydrocarbons components from hydrocarbon mixtures, there are several different systems for the subsequent separation of the solvent from the extracted hydrocarbon. In one system, for example, extracted aromatic hydrocarbon is removed from the selective solvent by water washing, sometimes known as springing. In another system, the extracted hydrocarbon may be removed from the selective solvent by distillation. Where it is possible to use an atmospheric distillation, when the character of both the selective solvent and the aromtic hydrocarbon being extracted permits such a distillation, this is generally a desired procedure since it is economical and both components are recovered in a dry state. With certain selective solvents the water springing is impossible since the solvent decomposes in the water. Such decomposition not only destroys the selective solvent but the reaction products may contaminate the hydrocarbon fraction extracted.

One commonly used selective solvent is gamma-butyrolactone, which may be used with 'or without water, showing a certain selectivity for aromatics from hydrocarbon mixtures, among other systems. Gamma-butyrolactone has a boiling point of about 204 C. which makes direct distillation of it from an aromatic extract in the gas-oil range impractical. Thus when using the gamma-butyrolactone to extract aromatic hydrocarbons from many hydrocarbon feeds, the gamma-butyrolactone must be washed with water or other antisolvent from the aromatic hydrocarbon. This, obviously, introduces a still further component into the system since the solvent is not simply recovered completely dry or completely free of the antisolvent. Many other solvents have been proposed in various systems, but in only a few instances are there any selective solvents which boil out of the gas-oil range and which will provide suflicient extraction for an economical system.

In one of the embodiments of the invention, beta-propiolactone has been found useful as a selective solvent for removing aromatic hydrocarbons from nonaromatic hydrocarbons in the gas-oil range. Furthermore, substituted beta-propiolactones and beta-propiolactams of the general formula wherein Y is selected from the class consisting of O and N-R R is selected from the class consisting of H and lower alkyl groups of from C to C and R is selected from the class consisting of hydrogen, halogen, nitrite, amine, and lower alkyl groups of from C to C are useful for selectively removing aromatic hydrocarbons from nonaromatic hydrocarbons.

An important object of the invention is to provide the separation of one class of hydrocarbons from dilfer- 7 hydrocarbons from gasoline boiling range aromatic and nonaromatic hydrocarbon mixtures.

It is a further object of the invention to provide a cyclic process for the separation of aromatic hydrocarbons in the gasoline boiling range aromatic and nonaromatic hydrocarbon feeds.

These and other objects and advantages of the invention may be accomplished 'by selective solvent extraction of a mixture of aromatic and nonaromatic hydrocarbons with a selective solvent selected from the class of beta-propiolactones and beta-propiolactams, which are cyclic compounds formed from certain beta-hydroxy and beta-amino acids.

In practice the hydrocarbon mixture containing the aromatic and nonaromatic hydrocarbons is thoroughly admixed with the desired selective solvent by any suitable means, as for example, mechanical agitation or in a countercurrent extraction column. On settling the two immiscible phases which are formed are then separated. The upper or rafiinate phase has an appreciably reduced content of the aromatichydrocarbons and the lower layer or phase contains the major amount of selective solvent which is substantially enriched in the aromatic hydrocarbons from the feed and a limited amount of nonaromatic hydrocarbons. The rafli nate may be recovered by washing with a small amount of water or distillation to remove residual amounts of the solvent dissolved therein. The extract phase may then he atmospheri-cally distilled to recover the aromatic free from the solvent.

The recovered solvent may then be used for subsequent extractions in a cyclic process. In modified procedure the extract phase may be washed with another hydrocarbon feed mixture, which is in a different boiling range, to provide a raffinate containing the aromatic hydrocarbon from the first feed mixture and which was originally dissolved in the solvent. This ratlinate is readily sepa rated by atmospheric distillation. The aromatic hydrocarbon from the second feed (now dissolved in the solvent) has replaced the original aromatic hydrocarbon mixture in the solvent, and it may then be recovered by distillation from the solvent or by mass action of an additional treatment with more of the original gasoline boiling range hydrocarbon mixture.

Following the latter mentioned procedure, a cyclic process may be derived wherein the hydrocarbon in the gasoline boiling range is initially passed through the selective solvent until the selective solvent is essentially saturated with the aromatic hydrocarbons. Then a mixture of hydrocarbons in a different boiling range may be passed through the aromatic-solvent mixture so that the aromatic hydrocarbons in the second hydrocarbon feed rep ace the aromatic hydrocarbons dissolved in the solvent until the aromatics from the second feed essentially saturate the selective solvent. The feed mixtures are passed through the. solvent phase until the aromatics in the incoming feed replaces the aromatics dissolved in the solvent. By alternately passing these feeds through the solvent, a cyclic process is provided wherein two different raffinates may be recovered each of which contains aromatics in a'different boiling range. This provides a system in which the aromatics are readily sepa} rated from the nonaromatics and recovered by a simple distillation process. In such processes it may be necessary to add small amounts of the selective solvent to replace the selective solvent dissolved in the raflinate leav ing the system.

Example I A portion of beta-propiolactone was shaken with a 50-50 toluene-n-heptane mixture having refractive index of 11 1.4400 at a two. to oneoil-to-solvent ratio. The recovered raffinate, which is the solvent lean phase, was- Patented Jan. 8, 1963 3 recovered from an extract (which is an aromatic rich solvent phase). On washing the ratfinate with water to remove the solvent from both of these phases, the following products were obtained, and the composition of these 4 When a similar amount of light catalytic cycle oil is shaken in a ratio of 2.5 to 1 oil-to-solvent ratio with gamma-butyrolactone, the following results:

are indicated from refractive index curve of known mix- 5 Volume of n 25 tures of the two, as is well known procedure: LOCO V01. per- Vol. per- Rainnate 79 1. 4916 cent of m, cent Aro- Aromatic Extract 22 1. 5795 Mixture matics Rafiinate 74.3 1.4278 38.7 When the light catalytic cycle oil is extracted with a Amman Extract 1'4743 2.5 to 1 oil-tosolvent ratio of 95% aqueous gamma- The solvent, however, has a boiling point which is essentially within the gasoline boiling range, that is about 162 C. The solvent, therefore, may not be recovered from the aromatics by direct distillation, but the mass action principle of exchange may be applied wherein a hydrocarbon mixture in a different boiling range may be passed through the aromatic-solvent mixture so as to replace the aromatic dissolved in the solvent with the aromatic in the second feed.

Example II A portion of beta-propiolactone was shaken with a reformate having a refractive index of n 1.4542 at a two to l oil-to-solvent ratio. The primary ratfinate, that is the solvent-lean phase, and a primary extract phase, that is the solvent-rich phase, were separated. On washing the samples of these phases with water to remove the solvent, the following products were obtained:

Vol. percent of m." Reformate Primary Ratfinate 89.2 1. 4496 Primary Aromatic Extract 10. 8 1. 4921 Example II] If the primary extract obtained from Example II is shaken with a light catalytic cycle oil at about a one to two primary extract phase to light catalytic cycle oil, a secondary raffinate and a secondary extract phase result. On washing these two phases with water to remove the solvent from the phases, the following products were obtained:

. 20 Secondary raffinate 1.5000 Secondary aromatic extract 1.5570

Example IV A portion of beta-propiolactone solvent is shaken with a light catalytic cycle oil (LCCO) in a ratio of about 2.5 to 1 volume of oil-to-solvent and raffinate and extract phases result. The two phases were separated and on washing with water to remove the solvent from these phases the following products were obtained:

Volume of 111,

Raffinate 88 1. 4990 Aromatic Extract 12 1. 5988 butyrolactone, however, the following results:

From these results it is readily seen that the beta-propiolactone is far superior to either gamma-butyrolactone or the aqueous gamma-butyrolactone in its selectivity for the aromatics. While its capacity is essentially the same as 95% aqueous gamma-butyrolactone, it is superior in its selectivity of the aromatics. Further, the beta-propiolactone boils at 162 making direct distillation from the extract phase feasible. On the other hand the gamma-butyrolactone boils at 204 C. and therefore must be washed from the extract with water.

I claim:

1. A process of obtaining an extract rich in aromatic hydrocarbons from a mixture of aromatic and non-aromatic hydrocarbons by means of a phase separation comprising extracting said hydrocarbon mixture with betapropiolactone, and separating the aromatic rich extract phase from the rafiinate phase.

2. A process of obtaining an extract rich in aromatic hydrocarbons from a mixture of aromatic and non-aromatic hydrocarbons in the gas-oil range by means of a phase separation, comprising extracting said hydrocarbon mixture with beta-propiolactone as the selective solvent, and then separating the aromatic rich extract phase from the raffinate phase.

3. A process for obtaining an extract rich in aromatics from a mixture of aromatic and non-aromatic hydrocarbons in the gas-oil range by means of a phase separation comprising extracting said hydrocarbon mixture with about a 2 to 1 oil-to-solvent ratio of beta-propiolactone as a solvent, and then separating the aromatic rich solvent phase from the rafiinate phase.

4. A process of obtaining an extract rich in aromatics from a mixture of aromatic and non-aromatic hydrocarbons in the gas-oil boiling range comprising extracting said hydrocarbon mixture having a first boiling range with beta-propiolactone as the selective solvent to form an extract rich in the aromatics in the gas-oil boiling range, extracting the resultant aromatic-rich solvent phase by adding a mixture of aromatic and non-aromatic hydrocarbons in a second boiling range different from boiling range of said gas-oil hydrocarbon mixture to thereby replace the aromatics of the gas-oil range dissolved in the solvent, and then distilling the resultant mixture containing aromatics from the gas-oil range mixture and the nonaromatics from the different boiling range mixture to thereby recover the gas-oil aromatics.

References Cited in the file of this patent UNITED STATES PATENTS 2,727,848 Georgian Dec. 20, 1955 2,831,905 Nelson Apr. 22, 1958 2.910.518 Lampert et a1 Oct. 27, 1959 2,917,562 Templeman et al Dec. 15, 1959 2,933,448 Morin et al Apr. 19, 1960 

4. A PROCESS OF OBTAINING AN EXTRACT RICH IN AROMATICS FROM A MIXTURE OF AROMATIC AND NON-AROMATIC HYDROCARBONS IN THE GAS-OIL BOILING RANGE COMPRISING EXTRACTING SAID HYDROCARBON MIXTURE HAVING A FIRST BOILING RANGE WITH BETA-PROPIOLACTONE AS THE SELECTIVE SOLVENT TO FORM AN EXTRACT RICH IN THE AROMATICS IN THE GAS-OIL BOILING RANGE, EXTRACTING THE RESULTANT AROMATIC-RICH SOLVENT PHASE BY ADDING A MIXTURE OF AROMATIC AND NON-AROMATIC HYDROCARBONS IN A SECOND BOILING RANGE DIFFERENT FROM BOILING RANGE OF SAID GAS-OIL HYDROCARBON MIXTURE TO THEREBY REPLACE THE AROMATICS OF THE GAS-OIL RANGE DISSOLVED IN THE SOLVENT, AND THEN DISTILLING THE RESULTANT MIXTURE CONTAINING AROMATICS FROM THE GAS-OIL RANGE MIXTURE AND THE NONAROMATICS FROM THE DIFFERENT BOILING RANGE MIXTURE TO THEREBY RECOVER THE GAS-OIL AROMATICS. 